Cruise control

Gtstorey

Goblin Guru
So if I have a resistor wired into my 3rd brake light, I am affecting what is being accomplished by the resistors in my DF button panel?

My current plan is to pull the resistor and check it the next time I can get on the road.
I think there is a check of the resistance of the brake light circuit/brake switch in the bcm or ECM that won’t pass if there are only led’s in the circuit so at least the newer models need a resistor. I think used a 100 ohm resistor.
This is independent of the switch circuit.
 

Sluggonaut

Goblin Guru
I have the 25W 100ohm resistor I found elsewhere on the forum installed with my LED 3rd brake light. I don't have cruise control with the switch in either position (not sure which way is on).

I also don't know if cruise control worked on the donor so there is that. It's not a big deal, I've just worked my way down my list of stuff to test and finally got to cruise control that was pretty far down that list.
 

Gtstorey

Goblin Guru
I will add that my cruise sort of works, but not very well. It engages but will overshoot when it needs to add throttle and after a few cycles of acceleration/overshoot/deceleration it cuts off. I think this is in the tune and shows up as a common problem on HP Tuners forum. The LNF has some “urgency” tables that may be causing this that I haven’t wanted to change since I’m happy with how it works otherwise and I rarely use cruise on any of my vehicles.
 

Gtstorey

Goblin Guru
You did wire the resistor in parallel not series?

I don’t know of a good way to diagnose the cruise without a Tech2 other than checking for voltage coming out of the cruise enable switch.
 

Sluggonaut

Goblin Guru
I followed these instructions when I added the resistor and 3rd brake light.

CHMSL blue wire to 3rd brake light positive wire and resistor wire. The other resistor wire and the negative 3rd brake light wire go to the rear ground stud. The 3rd brake light works, I just don't have cruise control.
 

Ark :D

Goblin Guru
As I understand it, the resistor you want for cruise control is a 50W, 6-ohm one. I wired in a different resistor (I forget now what it is) and my cruise does NOT work. I have a pair of 50W 6-ohm resistors here now and will wire one of them in soon.

*edit* I should add, the 50W 6-ohm is what DF is offering in their store, for this purpose.
 

Rauq

Goblin Guru
One of my switch pins had a tiny air gap between the wiring lead and the solder dot on the switch. Several hours of investigation, 15 second fix. I was all over the car looking for the problem, but it was the final 15 minutes of intentional effort with a multimeter at the switch panel that yielded results.
 

Gtstorey

Goblin Guru
I’m not sure what to think about the required resistor for the third brake light since it seems that a lot of different resistance values have worked other than maybe the logic check isn’t that picky.

the older models button circuits can be checked per the diagram posted by Ross. Disconnect at the bcm and check for resistance (c4-f9 to c2-61).
Open circuit when the cruise enable switch is off.
5250 ohms when the switch is on.
2400 ohms when the R/A switch is pushed and cruise is on.
1167 ohms when the S/C switch is pushed and cruise is on.
 

Ross

Goblin Guru
Aside from the resistors at the control switches, you also need the switches at the foot pedals to be working correctly. The clutch and brake switches can also cause cruise control to not work.
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Vehicle: 2006 Chevrolet Cobalt L4-2.0L SC VIN P
AllDataDIY
Vehicle » Diagrams » Electrical Diagrams » Cruise Control
 

Sluggonaut

Goblin Guru
Wouldn't there be starting issues (clutch switches) and brake light issues (brake switches) and not just cruise control issues if those switches had problems?
 

Ross

Goblin Guru
Cruise control has different switches on my car. The cruise switch is at the start of the pedal movement, while the engine start is at the bottom of the clutch pedal movement.
 

Chubbs

Well-Known Member
You did wire the resistor in parallel not series?

Which way is it supposed to be? In parallel?

I'm thinking this is my problem, I think (I'll have to check, it's been a while) I wired mine in parallel with the brake light. This effectively reduces the resistance, which doesn't seem like what we want to do. If we want the ECM to see an increased resistance across the third brake light, the resistor needs to be wired in series. Right?
 

Chubbs

Well-Known Member
Let's try this angle.

When the ECM is looking for a resistance value across the third brake light, what is it expecting to see? Is there an acceptable resistance rating range that will make cruise work?

I'm wondering if maybe some LED light assemblies have a different resistance than others. So perhaps a resistor that works on one car will not work on another if they have used a different third brake light. For example, if you were to reuse the stock third brake light, no resistor would be required at all, right?
 

Gtstorey

Goblin Guru
I haven’t seen anyone come up with a value that the resistance should be although it should be simple enough to measure on a donor car.
If you put the resistor in series with the light you will reduce the voltage on the light depending on the resistance added.
 

Gtstorey

Goblin Guru
In addition, I'm speculating that the BCM or ECM needs a résistance range (measured as a voltage drop) to check out, but it may have some other check that it needs to see.

This is why I said that trouble shooting the cruise control without a tech2 isn't easy.

I would confirm that your resistor is still good since a 10watt resistor sounds low and might have burned out. If that checks as still good, maybe get a 6ohm, 50watt resistor and try that since it's what DF uses. Maybe the older versions are pickier about what is used. This is assuming you have checked the voltage/resistance on the button panel.

Let's try this angle.

When the ECM is looking for a resistance value across the third brake light, what is it expecting to see? Is there an acceptable resistance rating range that will make cruise work?

I'm wondering if maybe some LED light assemblies have a different resistance than others. So perhaps a resistor that works on one car will not work on another if they have used a different third brake light. For example, if you were to reuse the stock third brake light, no resistor would be required at all, right?
 

Sluggonaut

Goblin Guru
If that checks as still good, maybe get a 6ohm, 50watt resistor and try that since it's what DF uses. Maybe the older versions are pickier about what is used.
Mine arrived yesterday and hope to get some time to install and test it before the weekend.
 

Chubbs

Well-Known Member
I'm taking another swing at this. I have replaced my 10w resistor with the DF recommended 6 ohm 50w resistor. The 10w was burned out, with one of the wires completely burned away from the resistor body.

So, with the new, bigger resistor, cruise still doesn't work. Also, the resistor gets HOT. Too hot to touch for more than half a second. I know resistors are supposed to be hot, but how hot is it supposed to get? It seems excessive, and makes me question if I have miswired something. The resistor is currently in parallel with the LED center brake light.
 

Gtstorey

Goblin Guru
What could be up to 32 watts will probably feel pretty warm. I'm surprised that something as small as 6ohms is used. There isn't much you can do to wire it wrong since it is basically line voltage through the resistor to ground. Rockauto listed the "high mounted brake" bulb as 13 watts which would be somewhere around 10-15 ohms. Of course there is still some resistance through the LED that would have to be calculated in parallel to try and match oem.

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